This invention relates to film circuits and in particular to a method of fabricating such circuits which permits thick film crossunders and thin film capacitors to be formed on the same substrate.
Thin film circuits offer significant advantages over most thick film and silicon integrated circuits where precision components are needed. In fabricating thin film circuits, just as in the integrated circuit field, a great deal of effort and attention has been directed to packing more components onto a substrate. This trend has necessitated use of some type of structure for bridging conductors when high density circuits are desired. Although several alternatives are available for this function, the most reliable appears to be the thick film crossunder. As known in the art of thin film circuit fabrication, such structures are typically formed by depositing a thick film electrode such as gold coupled to the thin film conductors to be bridged. One or more layers of a thick film dielectric such as glass layers are then deposited and fired and a thin film conductor formed thereover in a direction essentially orthogonal to the conductor being bridged.
While thick film crossunders have been used for thin film resistor circuits, it does not appear that they have been successfully incorporated into circuits including thin film capacitors. Among other reasons, this was apparently due to the incompatibility of firing cycles for the crossunder dielectrics and thick film electrodes with the standard capacitor components, especially the glass layer used for compensation of the roughness of the circuit substrate underlying the capacitor and the oxide underlay used to protect the glass layer.
It is therefore an object of the invention to provide a technique for the fabrication of film circuits which permits fabrication of thick film crossunders with thin film capacitors on the same substrate. It is a further object of the invention to provide a technique for incorporating thin and thick film components on a single substrate with a minimum number of processing steps.